1. Field of the Invention
The present invention relates to leak detection devices for packages and more particularly to leak detection devices utilizing helium detectors.
2. Discussion of the Background
Flexible packaging material such as that made of polymer or polymer derivatives has been widely used for packaging in many industries and especially the food industry. These materials can be manufactured in any size and shape and accordingly are advantageous to package manufacturing. However, some problems also occur due to the use of these materials. Since they are light and flexible, they are less resistant to puncturing, slicing and other problems than conventional metallic or glass material.
In one standard packaging process, the final sealing step is achieved by fusing similar materials which are used on both the lid and container. This creates a very safe seal which is nearly impossible to break. However, this creates problems for the consumer since there is great difficulty in opening such packages. In order to avoid marketing problems, seals have been made which are easier to open but which therefore have a greater chance of being unsealed. Problems in the defective seals may be due to wrinkles in the packaging, improper temperatures, contamination of the seal with extraneous material, absence of adhesive and variability of the sealant thickness.
Because of these reasons, the flexible packaging process is not completely reliable. In those packages which include a vacuum, seal defects allow air into the container. In those packages where a modified atmosphere is inserted, the gas contained in the headspace will leak out.
In order to ensure proper packaging, a number of detecting devices have been made so that improperly sealed packages can be rejected. Unfortunately, many of the leaks are too small to be detected by eye and, accordingly, this sophisticated equipment must be utilized.
One type of device shown in U.S. Pat. No. 4,747,299 includes a method of testing a seal by changing the external pressure around the seal. The change in position of the distended container wall in response to the pressure is then sensed.
Another device shown in U.S. Pat. No. 4,683,745 shows the application of a vacuum to a package with the measurement of the vacuum thereafter to determine if air has leaked into the vacuum from the container.
Another device shown in U.S. Pat. No. 4,205,551 includes a needle which is inserted into the package to apply pressure thereto. A sensor in the needle then determines if the pressure decreases.
Another device shown in U.S Pat. No. 4,715,215 includes a vacuum container for receiving the package. As the pressure is reduced, the package expands. If the size of the package decreases over time, a leak is indicated.
Other devices place a container under water in order to visually check for bubbles which escape from the container indicating a leak.
All of these testing devices are somewhat reliable but create problems in that they are too slow for inline testing and often require expensive equipment for varying the pressure around the container. In addition, trays having stiff bottoms and soft tops are not easily tested due to their construction. It is also difficult to detect leaks on the bottom of packages since they sit on a hard surface.
In other industries, leak detectors using gasses which can easily be sensed such as helium or carbon dioxide have been used. Helium, for example, has been used in a number of situations to detect very fine leaks in a process where fluids are carried or stored in pipes or vessels. Since helium is an inert gas, it can be used safely in conjunction with many materials. Also, helium sensors have a sensitivity which can detect the presence of helium at lower than 10.sup.-10 cc/second.